I need help with figuring out an equation

[Wallacegreen]

Hello, I’m in dire need of help.
here is the question

A kitchen Ring final circuit is wired in 2.5/1.5mm T&E and protected by a 32A type B circuit breaker. 70m of cable has been used.

Q1. What is the expected r1, r2, rn value ?

So far I’ve used the equation R=Mohms/m X Length =1,365.7 divided by 1000 = 1.36

what do I do with this number 1.36 to get the values ?

 

[Lucien Nunes]

You will need to consider the resistance per metre of the line / neutral and CPC separately as they are of different CSA.

 

[stevethesparks]

ρL/a
17.5/1000 x 70 / 2.5 or 1.5
2.5 = 0.49
1.5 = 0.81666
Roughly

 

[Wallacegreen]

ρL/a
17.5/1000 x 70 / 2.5 or 1.5
2.5 = 0.49
1.5 = 0.81666
Roughly

Hello is pL/a The equation R=pL/A

Still getting used to recognising certain things apologies.

 

[stevethesparks]

Yes
ρ being rho - (dependant on temperature) multiplied by length divided by cross sectional area

 

[Lucien Nunes]

One can either look up the resistance per unit length in a table or calculate it from the resistivity (ρ) of copper. For normal cables made to recognised standards such as T+E, I would suggest looking it up. Construction tolerances might make the tabulated value fractionally different from the theoretical minimum.

And @stevethesparks whilst I know what you mean by:

2.5 = 0.49

Its blatant falsehood as a mathematical expression gives it an air of naughtiness that we should not encourage amongst students! I would rather write longhand 'Resistance of 2.5mm² conductor = " etc.

 

[stevethesparks]

And @stevethesparks whilst I know what you mean by:

Its blatant falsehood as a mathematical expression gives it an air of naughtiness that we should not encourage amongst students! I would rather write longhand 'Resistance of 2.5mm² conductor = " etc.

Fair point - wrist slapped

 

[Wallacegreen]

One can either look up the resistance per unit length in a table or calculate it from the resistivity (ρ) of copper. For normal cables made to recognised standards such as T+E, I would suggest looking it up. Construction tolerances might make the tabulated value fractionally different from the theoretical minimum.

And @stevethesparks whilst I know what you mean by:

Its blatant falsehood as a mathematical expression gives it an air of naughtiness that we should not encourage amongst students! I would rather write longhand 'Resistance of 2.5mm² conductor = " etc.

Thankyou very much guys ! I enjoyed reading over the last part of that reply in particular. ?